1. Field of the Invention
The present invention relates to a lens barrel and an imaging apparatus.
2. Description of the Related Art
There has been proposed a lens barrel including a zoom mechanism that moves a plurality of lenses to a predetermined position by causing a linear cylinder to restrict the movement of a plurality of lens holding frames in the rotational direction while moving the plurality of lens holding frames for respectively holding the plurality of lenses in the optical axis direction by the rotation of a cam cylinder.
In order to meet the recent requirement for increasing an image-taking magnification, the number of lenses increases and a total extended length increases, resulting in a tendency with an increase in size of a lens barrel. On the other hand, there is also a requirement for thinning of a camera, and thus, the thickness of the camera when the lens barrel is retracted into the camera body needs to be reduced as much as possible.
In order to achieve thinning of a camera, it is contemplated that barrels in which the dimension is reduced in the optical axis direction are connected in a multi-stage configuration. However, there are many restrictions for disposing a plurality of cam grooves on a barrel without mutual intersection in terms of space.
On the other hand, bayonet grooves which are followed by bayonet protrusions provided on a linear cylinder are typically formed on the inner circumference of a cam cylinder. Then, the bayonet protrusion is mated with the bayonet groove so as to contact against both side wall surfaces of the bayonet groove in the width direction, so that the relative position restriction between the cam cylinder and the linear cylinder in the optical axis direction is achieved.
However, a plurality of cam grooves which are followed by the followers respectively provided on a plurality of lens holding frames is disposed on the inner circumference of the cam cylinder, a restriction may also occur in the space in which the bayonet groove is disposed.
Japanese Patent Laid-Open No. 2007-093999 discloses a lens barrel in which bayonet grooves are disposed along the circumferential direction of the cam cylinder so as to intersect a plurality of cam grooves formed on the inner circumference of the cam cylinder. Japanese Patent Laid-Open No. 2011-215279 discloses a lens barrel that restricts the relative position between the cam cylinder and the linear cylinder in the optical axis direction by sandwiching a portion between the image plane side wall surface of the bayonet groove and the image plane side end surface of the cam cylinder in the optical axis direction by the bayonet protrusion and the linear rib both provided on the linear cylinder at the TELE position.
In the lens barrel disclosed in Japanese Patent Laid-Open No. 2007-093999, the bayonet grooves must be disposed so as to intersect all of the cam grooves such that the bayonet protrusion steps over the cam groove when the bayonet protrusion passes through the cam groove. If the bayonet grooves are not disposed as described above, the bayonet protrusion is outside the bayonet groove when the bayonet protrusion passes through the cam groove, so that the relative position restriction cannot be made between the cam cylinder and the linear cylinder in the optical axis direction. Thus, the degree of freedom in selection of parts in which the cam grooves and the bayonet grooves are disposed on the inner circumference of the cam cylinder decreases, so that the lens barrel fails to correspond to various operations of lens groups.
In addition, in the lens barrel disclosed in Japanese Patent Laid-Open No. 2011-215279, the cam cylinder needs to rotate while avoiding the linear rib when the cam cylinder rotates relatively with respect to the linear cylinder, so that a restriction occurs in the arrangement of bayonet grooves.